1. Field of the Invention
The present invention relates to a gear reduction mechanism, and more particularly to a harmonic drive gear reduction mechanism.
2. Description of the Prior Art
FIG. 1 shows a conventional harmonic drive gear reduction mechanism disclosed in U.S. Pat. No. 7,178,427 B, which comprises a rigid inner spline 11, a flexible outer spline 12 disposed in the rigid inner spline 11, a flexible bearing 13 disposed in the flexible outer spline 12, and a wave generator 14 disposed in the flexible bearing 13. When the wave generator 14 rotates, it pushes against and makes the flexible bearing 13 and the flexible outer spline 12 deform, and as a result, the teeth at different parts of the deformed flexible outer spline 12 will be engaged with the teeth of corresponding part of the rigid inner spline 11, furthermore, the flexible outer spline 12 has less teeth than the rigid inner spline 11, so that a rotation speed reduction is achieved.
Since the wave generator 14 is elliptical, the flexible outer spline 12 driven by the wave generator 14 will also be deformed into an elliptical shape. However, the rigid inner spline 11 is circular, which makes the flexible outer spline 12 only engage at two points with the rigid inner spline 11, namely, only a few teeth are engaged, hence, the contact pressure and torque applied to each tooth are relatively big.
Many types of tooth, as shown in FIGS. 2-6, have been studied in the past in order to increase the number of teeth, however, the male tooth 15 and the female tooth 16 are much different in configuration from each other, which results in a relatively small contact area, large contact pressure and severe abrasion for each tooth, for example, the conventional harmonic drive gear reduction mechanism disclosed in U.S. Pat. No. 3,996,816 B as shown in FIG. 2, FIG. 3 shows a conventional harmonic drive gear reduction mechanism disclosed in U.S. Pat. No. 5,456,139 B, FIG. 4 shows a conventional harmonic drive gear reduction mechanism disclosed in U.S. Pat. No. 4,974,470 B, FIG. 5 shows a conventional harmonic drive gear reduction mechanism disclosed in U.S. Pat. No. 4,823,638 B, and FIG. 6 shows a conventional harmonic drive gear reduction mechanism disclosed in U.S. Pat. No. 8,028,603 B.
FIG. 7 shows a conventional harmonic drive gear reduction mechanism disclosed in U.S. Pat. No. 8,011,273 B, and FIG. 8 shows a conventional harmonic drive gear reduction mechanism disclosed in JPU-1978165179, wherein the wave generator 14 is also elliptical, therefore, it also suffers from the disadvantages as mentioned as above.
FIG. 9 shows a conventional harmonic drive gear reduction mechanism disclosed in JPA-1994174018, FIG. 10 shows a conventional harmonic drive gear reduction mechanism disclosed in JPA-1999094030, FIG. 11 shows a conventional harmonic drive gear reduction mechanism disclosed in JPU-1974140583, wherein the part 142 of the wave generator 14 abutting against the elongated shaft 141 is still elliptical, and the radius 143 of the elliptical part 142 is smaller than the diameter 144 of the elongated shaft 141, so that the flexible spline 12 which is driven by the wave generator 14 only engage at two points with the rigid inner spline 11, namely, only a few teeth are engaged. Hence, the contact pressure and torque applied to each tooth are relatively big.
FIGS. 12, 13 show a conventional harmonic drive gear reduction mechanism disclosed in JPA-2012251603, wherein the profile of the wave generator 14 consists of three arc-shaped sections which simulate an ellipse. However, the angle α for the arc-shaped section which has the radius R1 is only 5 degrees, therefore, the structural strength of the wave generator is limited.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.